Automatic signature verification

Abstract

A method and apparatus for automatically verifying a signature of an individual is described. The apparatus digitizes an image of the signature and provides a grey scale representation of each pixel. Next, the apparatus determines parameters of this digitized image and compares them to corresponding reference parameter values which were determined from a valid signature. The results of the comparison indicate if the signature to be verified is valid. The parameters include a center of gravity of the pixels within each row and columns of the digitized image, a center of gravity line for the centers of gravity for the rows or columns and the center of gravity for all pixels of the image. Other parameters include the positions of maximum grey scale pixels within each row or column, sums of grey scale values per column or row and the shape of a bow within the signature image.

We claim: 
     
       1. A method for automatically verifying a person's signature on a check or other document, said method comprising the steps of: storing in a memory one or more references defining one or more respective characteristics of a value signature of said person;   digitizing an image of the signature to be verified, the digitized image representing grey scale levels of a multiplicity of image elements;   using a computer system, determining a center of gravity line in a direction for the digitized image by determining a plurality of centers of gravity of the pixels perpendicular to said direction at respective spaced locations in said direction using the grey scale levels as weighting factors for the respective pixels, and then determining said center of gravity line based on said plurality of centers of gravity;   using a computer system, comparing said center of gravity line to said one or more stored references for the valid signature; and   using a computer system, determining validity of the signature to be verified based on the comparing step; and if said signature is determined to be invalid, rejecting said check or other document, and   if said signature is determined to be valid, accepting said check or other document.     
     
     
       2. The method of claim 1 wherein said center of gravity line is determined by linear regression of said plurality of centers of gravity. 
     
     
       3. The method of claim 1 further comprising the step of digitizing an image of said valid signature for storage in said memory. 
     
     
       4. The method of claim 1 wherein said one or more references are based on a valid signature that is aligned with a horizontal line and further comprising the step of aligning the digitized image of said signature to be verified with a horizontal line. 
     
     
       5. The method of claim 1 wherein the stored reference is scaled to a reference size of said valid signature; and   the digitizing step comprises the step of normalizing the digitized image with respect to the reference size of said valid signature.   
     
     
       6. The method of claim 1 wherein the step of determining a center of gravity line comprises the step of determining each of said centers of gravity based on a pixel along a line perpendicular to said direction and passing through the respective spaced location, said pixel having a maximum grey scale level along said line.   
     
     
       7. Apparatus for verifying a person's signature on a check or other document, said apparatus comprising: means for storing one or more references defining one or more respective characteristics for a valid signature of said person;   means for digitizing an image of the signature to be verified, the digitized image representing grey scale levels of a multiplicity of pixels;   means for determining a center of gravity line in a direction for the image by determining a plurality of centers of gravity of the pixels perpendicular to said direction at respective spaced locations in said direction using the grey scale levels as weighting factors for the respective pixels, and then determining said center of gravity line based on said plurality of centers of gravity; and   means for comparing said center of gravity line to corresponding reference(s) for the valid signature to determine if said signature is valid, and if said signature is determined to be invalid, rejecting said check or other document, and   if said signature is determined to be valid, accepting said check or other document.     
     
     
       8. Apparatus as set forth in claim 7 wherein said center of gravity line is determined by linear regression of said plurality of centers of gravity. 
     
     
       9. Apparatus as set forth in claim 7 further comprising means for aligning said digitized image with a horizontal reference. 
     
     
       10. Apparatus as set forth in claim 7 wherein each of said plurality of centers of gravity is based on substantially all pixels along a respective line perpendicular to said direction and passing through the respective spaced location. 
     
     
       11. The method of claim 1 further comprising the steps of: determining a position of a pixel having a maximum grey scale value for each of a plurality of parallel lines through said image;   comparing said positions of the maximum grey scale pixels for said plurality of lines to corresponding reference(s) for the valid signature; and   using a computer system, determining validity of the signature to be verified based on the comparison of said positions of the maximum grey scale pixels.   
     
     
       12. The method of claim 1 wherein each of said plurality of centers of gravity is based on substantially all pixels along a respective line perpendicular to said direction and passing through the respective spaced location. 
     
     
       13. The method of claim 11 further comprising the step of aligning the digitized image of said signature with a horizontal reference. 
     
     
       14. The method of claim 11 further comprising the step of normalizing the digitized image with respect to a size of said valid signature. 
     
     
       15. The method of claim 11 wherein the position determining step comprises the step of calculating said maximum grey scale values for each column or row of the digitized image. 
     
     
       16. Apparatus as set forth in claim 7 further comprising: means for determining a position of a pixel having a maximum grey scale value for each of a plurality of parallel lines through said image; and   means for comparing said positions of the maximum grey scale pixels for said plurality of lines to corresponding reference(s) for the valid signature to determine if the signature to be verified is valid.   
     
     
       17. Apparatus as set forth in claim 16 further comprising means for aligning the digitized image of said signature with a horizontal reference. 
     
     
       18. Apparatus as set forth in claim 16 wherein the determining means determines the maximum gray scale value for each column and row of the digitized image. 
     
     
       19. A method as set forth in claim 1 further comprising the steps of: determining sums of grey scale levels for pixels in each of a plurality of rows or columns;   comparing said sums to corresponding references for the valid signature; and   determining validity of the signature to be verified based on the comparison of said sums.   
     
     
       20. The method of claim 19 further comprising the step of digitizing an image of said valid signature for storage in said memory. 
     
     
       21. The method of claim 19 further comprising the step of aligning the digitized image with respect to a horizontal reference. 
     
     
       22. The method of claim 19 wherein only the sums which exceed a threshold are compared to the corresponding reference. 
     
     
       23. Apparatus as set forth in claim 7 further comprising: means for determining sums of grey scale levels for pixels in each of a plurality of rows or columns; and   means for comparing said sums to corresponding references for the valid signature; and   means for determining validity of the signature to be verified based on the comparison of said sums.   
     
     
       24. Apparatus for verifying a person's signature on a check or other document, said apparatus comprising: means for storing one or more references defining one or more respective characteristics of a valid signature for said person;   means for digitizing an image of the signature to be verified, the digitized image representing a multiplicity of image elements (pixels);   means for representing a shape of a bow within the digitized image of said signature with an equation of at least second order which approximates said bow;   means for comparing the representation of said shape of said bow to the reference for the valid signature; and   means for determining validity of the signature to be verified based on the comparison; and if said signature is determined to be invalid, rejecting said check or other document, and   if said signature is determined to be valid, accepting said check or other document.     
     
     
       25. Apparatus as set forth in claim 24 wherein the representing means determined sums of pixels within each of a plurality of columns or rows through said bow, identified two peaks of said sums within the rows or two peaks of said sums within the columns, and uses said two peaks as points on a curve defined by said second order equation. 
     
     
       26. Apparatus as set forth in claim 24 wherein the representing means determines positions of extreme left and right pixels of said bow. 
     
     
       27. Apparatus as set forth in claim 24 wherein the digitizing means determines a grey scale level for each of said pixels, and the representing means determines a shape of said bow by summing grey scale levels of pixels in each column of pixels of said bow.